The present invention relates to a synchrotron apparatus for accelerating or storing particle beams.
The basic arrangement of a conventional synchrotron apparatus which has been disclosed, for example, in "Superconducting Racetrack Electron Storage Ring and Coexistent Injector Microtron for Synchrotron Radiation" of TECHNICAL REPORT of ISSP Ser. B No. 21, September 1984 by Yoshikazu Miyahara et al. is shown in FIG. 1. This synchrotron apparatus is composed of a loop-shaped vacuum chamber 7 through which a beam of charged particles passes, an RF accelerating cavity 2 for accelerating the electron beam, a pair of focusing magnets 3a for focusing the electron beam, a pair of defocusing magnets 3b for defocusing the electron beam, and a pair of bending magnets 4 for bending the electron beam. These components together form an electron storage ring. The electron beam accelerates along a balanced orbit 1 which is a closed orbit determined by the energy of the electron beam and the magnetic field intensities of the focusing magnets 3a, the defocusing magnets 3b, and the bending magnets 4. In the electron storage ring indicated by the balanced orbit 1, energy loss, which occurs from generation of synchrotron radiation at the moment the electrons are being bent, is replenished by the RF accelerating cavity 2 to continuously store electrons having a certain energy level. However, the energy levels of each electron disperse in an energy band having a certain width (called energy dispersion hereafter). How this energy dispersion is determined will be explained below.
The above energy dispersion can be thought of by converting the time of arrival of the electrons at RF accelerating cavity 2 to a phase of RF voltage. The phase at which radiation energy or the energy loss per one round of the electron is equivalent to an RF voltage or an acceleration of the electrons resulting from replenishment by the RF accelerating cavity 2, is represented by .phi..sub.0. If the energy of an electron is higher than a standard level for some reason, the electron circles around an orbit outside of the balanced orbit 1. In this case, when the electron arrives at the RF accelerating cavity 2, it is in a slight phase lag condition, that is the phase angle is delayed more or less in regard to the phase .phi..sub.0, so that the acceleration voltage becomes less than the energy loss from radiation. Accordingly, the energy of the electron gradually decreases every circulation. On the other hand, in case of an electron having less energy than the standard level, the inverse phenomenon occurs, whereby the energy of the electron is increased. Therefore in relation to the high-frequency phase, the electrons oscillate (synchrotron oscillation) around the standard phase .phi..sub.0. Practically, however, since the radiation energy of the particle per circuit is in proportion to the square of the energy of the particle, a kind of damping is added to the above oscillation (synchrotron damping). Accordingly, the energy dispersion of the electrons in the ring is determined by the balance between the energy fluctuation of each electron from the synchrotron radiation and the synchrotron damping. As a result, the energy dispersion is in inverse proportion to the square root of the radius of curvature of the bending magnets 4.
As noted, in the synchrotron apparatus it is often necessary to make the energy dispersion as small (narrow) as possible. If the energy dispersion is large (wide) due to a small square root of the radius of curvature of the bending magnet 4 according to the prior art arrangement, the electron beam orbit expands to bring a diminution (decrease) in particle density because the beam path broadens, the beam cross section increases, and the beam length lengthens. Accordingly, this brings a decrease in collision frequency between particles in particle beam collision experiments. In order to overcome this drawback, it is necessary to store a very large current, and problems such as instability of the particle beam occurs. Further if the beam diameter increases, it is necessary to enlarge vacuum vessels through which the beam passes and to expand the effective magnetic field areas, causing increases in size of the total apparatus and creating problems in relation to cost and area used by the apparatus.